How to create a custom URL for my Google+ Page?

Hello everyone! I hope someone help. I have many times to make a custom url for my Google+ page but it doesn't work. Even if it looks on the links fine, but when I click on it gives an error. This is the page link: https://plus.google.com/109897519859046287742 The steps that I followed: Went to About sections, Links, changed URL and then nothing happened. So how to create a costume URL?! Thank you! Mena Naqada Music